linux/mm
Nick Piggin 945754a175 mm: fix race in COW logic
There is a race in the COW logic.  It contains a shortcut to avoid the
COW and reuse the page if we have the sole reference on the page,
however it is possible to have two racing do_wp_page()ers with one
causing the other to mistakenly believe it is safe to take the shortcut
when it is not.  This could lead to data corruption.

Process 1 and process2 each have a wp pte of the same anon page (ie.
one forked the other).  The page's mapcount is 2.  Then they both
attempt to write to it around the same time...

  proc1				proc2 thr1			proc2 thr2
  CPU0				CPU1				CPU3
  do_wp_page()			do_wp_page()
				 trylock_page()
				  can_share_swap_page()
				   load page mapcount (==2)
				  reuse = 0
				 pte unlock
				 copy page to new_page
				 pte lock
				 page_remove_rmap(page);
   trylock_page()
    can_share_swap_page()
     load page mapcount (==1)
    reuse = 1
   ptep_set_access_flags (allow W)

  write private key into page
								read from page
				ptep_clear_flush()
				set_pte_at(pte of new_page)

Fix this by moving the page_remove_rmap of the old page after the pte
clear and flush.  Potentially the entire branch could be moved down
here, but in order to stay consistent, I won't (should probably move all
the *_mm_counter stuff with one patch).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Acked-by: Hugh Dickins <hugh@veritas.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-06-23 11:28:32 -07:00
..
Kconfig PAGEFLAGS_EXTENDED and separate page flags for Head and Tail 2008-04-28 08:58:22 -07:00
Makefile uaccess: add probe_kernel_write() 2008-04-17 20:05:36 +02:00
allocpercpu.c cpumask: Cleanup more uses of CPU_MASK and NODE_MASK 2008-04-19 19:44:58 +02:00
backing-dev.c mm: bdi: fix race in bdi_class device creation 2008-05-20 13:31:53 -07:00
bootmem.c Add return value to reserve_bootmem_node() 2008-06-21 11:25:10 -07:00
bounce.c block: Initial support for data-less (or empty) barrier support 2007-10-16 11:03:56 +02:00
dmapool.c dmapool: enable debugging for CONFIG_SLUB_DEBUG_ON too 2008-04-28 08:58:20 -07:00
fadvise.c xip: support non-struct page backed memory 2008-04-28 08:58:23 -07:00
filemap.c mm: fix infinite loop in filemap_fault 2008-05-14 19:11:13 -07:00
filemap_xip.c xip: support non-struct page backed memory 2008-04-28 08:58:23 -07:00
fremap.c mm: fix various kernel-doc comments 2008-03-19 18:53:35 -07:00
highmem.c mm: highmem kernel-doc additions 2008-03-19 18:53:35 -07:00
hugetlb.c hugetlb: fix lockdep error 2008-06-06 11:29:09 -07:00
internal.h memory hotplug: free memmaps allocated by bootmem 2008-04-28 08:58:26 -07:00
maccess.c kgdb: fix optional arch functions and probe_kernel_* 2008-04-17 20:05:39 +02:00
madvise.c xip: support non-struct page backed memory 2008-04-28 08:58:23 -07:00
memcontrol.c memcg: simple stats for memory resource controller 2008-05-01 08:04:02 -07:00
memory.c mm: fix race in COW logic 2008-06-23 11:28:32 -07:00
memory_hotplug.c memory_hotplug: always initialize pageblock bitmap 2008-05-14 19:11:15 -07:00
mempolicy.c mempolicy: use struct mempolicy pointer in shmem_sb_info 2008-04-28 08:58:25 -07:00
mempool.c spelling fixes: mm/ 2007-10-20 01:27:18 +02:00
migrate.c Reinstate ZERO_PAGE optimization in 'get_user_pages()' and fix XIP 2008-06-20 11:18:25 -07:00
mincore.c mm: remove nopage 2008-04-28 08:58:18 -07:00
mlock.c do not limit locked memory when RLIMIT_MEMLOCK is RLIM_INFINITY 2007-07-16 09:05:37 -07:00
mmap.c brk: make sys_brk() honor COMPAT_BRK when computing lower bound 2008-06-06 11:29:09 -07:00
mmzone.c mm: filter based on a nodemask as well as a gfp_mask 2008-04-28 08:58:19 -07:00
mprotect.c mprotect: prevent alteration of the PAT bits 2008-05-14 19:11:15 -07:00
mremap.c sparse pointer use of zero as null 2007-10-18 14:37:31 -07:00
msync.c Detach sched.h from mm.h 2007-05-21 09:18:19 -07:00
nommu.c nommu: Correct kobjsize() page validity checks. 2008-06-12 07:56:17 -07:00
oom_kill.c oom_kill: remove unused parameter in badness() 2008-04-28 08:58:26 -07:00
page-writeback.c mm: Add NR_WRITEBACK_TEMP counter 2008-04-30 08:29:50 -07:00
page_alloc.c mm: Minor clean-up of page flags in mm/page_alloc.c 2008-06-09 10:22:24 -07:00
page_io.c mm: fix PageUptodate data race 2008-02-05 09:44:19 -08:00
page_isolation.c memory hotremove: unset migrate type "ISOLATE" after removal 2007-11-14 18:45:38 -08:00
pagewalk.c pagemap: pass mm into pagewalkers 2008-06-12 18:05:41 -07:00
pdflush.c mm/pdflush.c: merge the same code in two path 2008-05-13 08:02:24 -07:00
prio_tree.c spelling fixes: mm/ 2007-10-20 01:27:18 +02:00
quicklist.c quicklists: Only consider memory that can be used with GFP_KERNEL 2008-01-14 08:52:22 -08:00
readahead.c mm: bdi: export BDI attributes in sysfs 2008-04-30 08:29:49 -07:00
rmap.c mm: remove nopage 2008-04-28 08:58:18 -07:00
shmem.c mm: bdi: add separate writeback accounting capability 2008-04-30 08:29:50 -07:00
shmem_acl.c [PATCH] Fix typos in mm/shmem_acl.c 2006-10-11 11:14:23 -07:00
slab.c Slab: Fix memory leak in fallback_alloc() 2008-06-21 16:51:02 -07:00
slob.c slob: Fix to return wrong pointer 2008-05-19 20:55:25 +03:00
slub.c slub: ksize() abuse checks 2008-05-22 19:52:18 +03:00
sparse-vmemmap.c NULL noise: fs/*, mm/*, kernel/* 2008-03-30 14:18:41 -07:00
sparse.c revert "memory hotplug: allocate usemap on the section with pgdat" 2008-04-30 08:29:55 -07:00
swap.c mm: fix atomic_t overflow in vm 2008-05-24 09:56:09 -07:00
swap_state.c mm: bdi: add separate writeback accounting capability 2008-04-30 08:29:50 -07:00
swapfile.c mm: use non-racy method for /proc/swaps creation 2008-04-29 08:06:20 -07:00
thrash.c Bug in mm/thrash.c function grab_swap_token() 2007-05-11 08:29:32 -07:00
tiny-shmem.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6 2008-03-25 08:57:47 -07:00
truncate.c fix invalidate_inode_pages2_range() to not clear ret 2008-04-28 08:58:18 -07:00
util.c fix mm/util.c:krealloc() 2007-11-14 18:45:41 -08:00
vmalloc.c docbook: fix vmalloc missing parameter notation 2008-05-01 08:03:59 -07:00
vmscan.c mm: fix incorrect variable type in do_try_to_free_pages() 2008-06-12 18:05:39 -07:00
vmstat.c make vmstat cpu-unplug safe 2008-05-13 08:02:23 -07:00